There has long been an interest in apparatus useful in the separation of solid materials from liquids in which the solid materials are suspended. Such apparatus have applications in diverse fields, such as the handling of commercial and municipal wastes, beet sugar manufacture, coal and uranium mining, phosphate rock processing and the like.
U.S. Pat. No. 3,523,889 describes one such apparatus for rapidly and continuously separating suspended solid materials from liquids. The apparatus described was a marked departure from the prior art in that it involved the introduction of liquid influent feed containing freshly agglomerating solids at a location near the bottom of the separating tank or apparatus and below the level of previously agglomerated solids. By means of this apparatus, a dynamic sludge bed was created in which particles after being dispersed radially outward collide with other agglomerated particles to cause still further agglomeration and settling. This brought about substantial improvement in the throughput of solid materials to be recovered.
In spite of the improved results obtained with the apparatus of U.S. Pat. No. 3,523,889, there is a theoretical limit for a given unit or apparatus on the throughput and recovery of solids. In order to increase throughput larger and larger units have been built. The erection and operation of large units have created problems in the realization of expected increased throughput. Efforts have been made to introduce the influent feed at more than one point within the tank. These efforts led to various feedwell structures, including annular feedwells, such as the one disclosed in Australian Pat. No. 421,865.
This patent describes a sedimentation apparatus having an annular feedwell through which liquid feed containing suspended solids is carried to an upper portion of the tank above the level of previously settled solids. Upon leaving the feedwell, influent feed strikes downwardly-angled deflecting plates and is dispersed within the tank.
In the present invention, it has been found that by using an annular feedwell which delivers influent feed to a position near the bottom of a settling tank, at which position the influent feed is deflected radially outward and inward by a substantially horizontal concentric annular baffle, it is possible to maintain a substantially uniform dynamic sludge bed in settling tanks of large diameter and to achieve a high throughput of solids per unit area of settling tank. It has also been found that by using an annular feedwell with associated planar horizontal baffle plate it is possible to effect a more even distribution of feed and solids to be settled throughout the tank.